Google diverted hundreds of flights to cut global warming contrails

A court case involving thousands of flights between the US and Europe has found that planes produce fewer flies if they follow flight paths recommended by an artificial intelligence to reduce their global warming effect.

The contrails triggered by soot particles produced by aircraft engines are believed to cause more warming than the carbon dioxide emitted by aircraft. Research has also shown that some ice-rich regions in the upper atmosphere are more likely to form contrails when a plane passes through them, and that AI can predict where these regions will be using detailed weather forecasts.

There have been small-scale trials showing that aircraft diverted through these regions will produce fewer contrails, but the practice has yet to be applied to large-scale commercial flights.

Now, Dinesh Sanekommu at Google and his colleagues have used an AI contrail forecasting tool to provide routing advice in a randomized control sample of more than 2,400 real American Airlines flights.

The trial involved flights heading east from the US to Europe and ran for around 17 weeks, from January to May 2025. The direction was only one way because these flights would take place at night, which is when contrails have been found to have a more pronounced heating effect. During the day, bars can have a cooling effect because they reflect sunlight back into space.

Each flight route between two cities was randomly assigned to one of two groups. For the first group, air traffic controllers had an option in their flight planning software to choose an AI-optimized route with a low trajectory, but for the second, no option was suggested.

Although dispatchers in the first group always had the option of choosing a low-path route, only 112 of 1,232 flights in this group actually ended up taking the alternative route due to operational concerns, such as cost or safety, says Sanekommu.

According to an AI analysis of satellite imagery of flight paths, there was a 62 percent lower amount of visible contours for flights that took the contrail-optimized route suggested to air traffic controllers. When all flights that had the opportunity to take a contrail-optimized route are included, the effective total reduction in contrail formation was 11.6 percent compared to the control group.

“It validated the thesis that if we could figure out how to safely and correctly integrate into the flight planning process, then this is a scalable route to assess counterattack avoidance across many flights,” says Sanekommu.

The team estimates that the flights’ warming effect was reduced by 13.7 percent in the entire group given a proposed route and 69.3 percent in the flights that took the optimized route. There was no difference in fuel consumption between the groups.

“This is probably the best you can do, at least with the tools we currently have,” says Edward Gryspeerdt of Imperial College London. “It suggests that this is possible. The 62 percent reduction in satellite-observed lines that they see is unlikely to have happened by chance.”

However, it is unclear how much the 11.6 percent figure can be improved in real operations, due to the difficulties of flight planning, says Gryspeerdt. “You can’t necessarily just scale this up to be a 60 percent reduction in contrails from every flight everywhere, but even a 10 percent reduction in contrails is still a not insignificant effect.”